1. Field of the Invention
The present invention relates to a fuel cell system and method for controlling the same for starting up the fuel cell system appropriately in accordance with various conditions of the fuel cell.
2. Description of the Related Art
In some cases, a solid polymer electrolyte membrane fuel cell has a problem with cross leak, which is a phenomenon in which a fuel (anode gas) permeates from anode to a cathode through an electrolyte membrane, and an oxidant (cathode gas) permeates from the cathode to the anode through the electrolyte membrane while no electric power is being generated from the fuel cell. As widely known, if this phenomenon occurs, the amount of fuel remaining inside the anode decreases; and therefore, the concentration of the fuel inside the anode decreases accordingly. As a countermeasure for this phenomenon, a gas remaining inside the anode of a fuel cell is replaced with anode gas when starting up the fuel cell. (See, for example, Japanese Patent Laid-open Publication No. 2003-331888, paragraphs [0015] to [0018] and FIG. 1.)
The inventors of the present invention found that the amount of anode gas remaining inside the anode of a fuel cell is not constant when starting up the fuel cell; that is, the amount of anode gas remaining inside the anode of the fuel cell varies according to ambient temperature or according to a fuel cell operation when stopping electric power from being generated in the fuel cell. More specifically, if the concentration of the anode gas is high inside the anode, a fewer amount of anode gas may be supplied anew for replacing a scavenging gas remaining inside the anode when starting up the fuel cell. Conversely, if the concentration of the anode gas is low inside the anode, a greater amount of anode gas must be supplied anew for replacing a scavenging gas remaining inside the anode when starting up the fuel cell. However, no method has been considered for adjusting the amount of anode gas according to the concentration of the anode gas remaining inside the anode.